A. Field of the Invention
This invention relates generally to single particle absorption spectrometry and more particularly to spectrometry in which a caloric technique is used to measure the absorption spectra for a single aerosol particle.
B. Description of the Prior Art
In this application several publications are referenced by Arabic numerals in parentheses. Full citations for these publications may be found at the end of the written description immediately preceding the claims. The disclosures of all such publications, in their entireties, are hereby expressly incorporated by reference in this application as if fully set forth, for purposes of indicating the background of the invention and illustrating the state of the art.
Recent experiences in the Gulf War and with the Sarin poisonous gas attack in a Japanese subway, have demonstrated the susceptibility of both military and civilian personal to chemical/biological aerosol attacks and the need to develop some type of early warning system. Current methods for real time biological aerosol detection attempt to exploit the relatively weak fluorescence phenomena inherent in all living materials. Unfortunately, measured fluorescent spectra are often quite broad and featureless, making species discrimination and/or identification nearly impossible. It has become apparent that additional criteria must be considered, i.e., absorption, if effective identification schemes are to be developed.
In addition, researchers have proposed sophisticated models that might be able to predict how complex aerosols such as soot (important in predicting global warming) and spore cells (the types of aerosols encountered in biological warfare) absorb electromagnetic energy at certain frequencies, but have expressed frustration in not having good experimental data to compare.(2,3,4)
At the heart of these problems is the absence of detailed absorption spectra derived directly from in situ aerosols, preferably a single particle. This lack of detailed information for certain aerosols arises from the fact that all prior scientific studies involving absorption have used a conventional photoacoustic approach in which an ensemble or distribution of aerosol particles are used in the measurement. (5,6,7) This conventional approach has one major drawback: measurements conducted on an ensemble distribution of aerosols, even those with the most narrow of size distributions, severely mask fine detailed structures inherent in the absorption spectra due to averaging effects over both size and spatial orientation of the particles.(8)
Another weak point associated with conventional methods is that it is impossible to conduct a detailed study involving specific particle morphology (e.g., the type of study one would like to conduct when considering single cell organisms) when an ensemble approach is considered. Because this apparatus/technique can derives absorption spectra from a single aerosol particle, it is uniquely suited for detection schemes that require functionality at extremely low aerosol densities. Thus, for all practical purposes, to date there have been no rapid, reliable, effective means for early detection of bioaerosols that could be used to warn populations at risk in sufficient time to take evasive measures.